Evidence for quasi-two-dimensional superconductivity in electron-doped Li0.48(THF)yHfNCl

Dc-magnetization and NMR measurements were carried out on a layered superconductor Li0.48(THF)yHfNCl having Tc∼26 K. For the magnetic field applied perpendicular to the basal plane (ab plane) above 10 kOe, we found a pronounced broadening of the superconducting transition in temperature dependence of magnetization and the substantial diamagnetic signals were observed as high as 2Tc, indicating the existence of superconducting fluctuations. Analysis based on the anisotropic Ginzburg-Landau model reveals that the present system is a highly anisotropic superconductor. 7Li-NMR signals were observed around zero Knight shift, indicating that the local Fermi-level density of states, N(EF), at Li site is practically nothing and the superconductivity is derived from the HfNCl layer. We have shown the unambiguous evidence for the quasi-two-dimensional superconducting character in this system.